The present invention relates to subterranean cementing operations, and more particularly, to improved casing strings, and methods of using such improved casing strings in subterranean cementing operations.
Hydraulic cement compositions commonly are utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings, such as casings and liners, are cemented in well bores. In typical primary cementing operations, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Conventionally, two common pumping methods have been used to place the cement composition in the annulus. First, the cement composition may be pumped down the inner diameter of the pipe string, out through a casing shoe and/or circulation valve at the bottom of the pipe string and up through the annulus to its desired location. This is referred to as a conventional-circulation direction method. Second, the cement composition may be pumped directly down the annulus so as to displace well fluids present in the annulus by pushing it through the casing shoe and up into the inner diameter of the pipe string. This is referred to as a reverse-circulation direction method.
In reverse-circulation methods, it is generally undesirable for the cement composition to enter the inner diameter of the pipe string from the annulus through the casing shoe and/or circulation valve. This often is the case, because any resultant set cement typically must be drilled out before further operations are conducted in the well bore. The drill out procedure may be avoided by preventing the cement composition from entering the inner diameter of the pipe string through the casing shoe and/or circulation valve.